Heat oil in a large saucepan over medium-high heat. Sauté onion and chorizo until onion has softened, 2 to 3 min. Add garlic and rice, stirring to coat rice in oil. Stir in tomatoes and broth and bring to a boil. Reduce heat, cover and simmer until all the liquid is absorbed, about 15 min.
Remove from heat; gently stir in black beans and corn. Cover and let stand 5 min. Garnish with green onions.